X-ray diagnostic apparatus

ABSTRACT

An X-ray diagnostic apparatus according to an embodiment includes a support frame and processing circuitry. The support frame supports an X-ray generator and an X-ray detector. The processing circuitry is configured to, when rotational acquisitions are performed multiple times after a contrast agent is injected one time, previously set a generation condition of an X-ray that is generated by the X-ray generator for each of the rotational acquisitions, the rotational acquisitions being performed while the support frame is rotated around a subject.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-097161, filed on May 8, 2014, theentire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an X-ray diagnosticapparatus.

BACKGROUND

There is a conventionally-known technology of X-ray diagnosticapparatuses for performing rotational acquisition multiple times after acontrast agent is injected and reconstructing a three-dimensional imagefrom image data that is acquired during each rotational acquisition. Forexample, with the above-described technology, after a contrast agent isinjected, rotational acquisitions are performed multiple times toacquire projection data at a predetermined frame rate while an arm thatsupports an X-ray generator and an X-ray detector is rotated, andthree-dimensional volume data is reconstructed from the projection datathat is acquired during each rotational acquisition. Thus, with theabove-described technology, acquisitions (for example, an acquisitionduring CT-like imaging of hepatic arteriography for a diagnosis of ahepatic tumor and the following acquisition during CT-like imaging at alater phase (alternatively, an acquisition of corona enhancement arounda hepatocellular tumor)) at multiple time phases can be performed duringone-time contrast injection, and invasiveness for patients by imagingcan be reduced. However, with the above-described conventionaltechnology, it is sometimes difficult to acquire the optimum image dataduring each rotational acquisition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates an example of the configuration ofan X-ray diagnostic apparatus according to a first embodiment;

FIG. 2 is a flowchart that illustrates an example of the steps of theoperation of the X-ray diagnostic apparatus according to the firstembodiment;

FIG. 3 is a diagram that illustrates an example of a rotationalacquisition of the X-ray diagnostic apparatus according to the firstembodiment;

FIG. 4 is a diagram that illustrates an example of a display imageaccording to the first embodiment;

FIG. 5 is a diagram that illustrates an example of an acquisition byusing correction data according to a modified example 5;

FIG. 6 is a diagram that illustrates an example of generation ofcorrection data according to the modified example 5;

FIG. 7 is a diagram that illustrates an example of correction dataaccording to the modified example 5; and

FIG. 8 is a diagram that illustrates an example of a rotationalacquisition of the X-ray diagnostic apparatus according to a secondembodiment.

FIG. 9 is a diagram that illustrates an example of the configuration ofan X-ray diagnostic apparatus according to another embodiment.

DETAILED DESCRIPTION

With reference to the drawings, a detailed explanation is given below ofan X-ray diagnostic apparatus according to an embodiment. Furthermore,there is no limitation on the embodiment that is described below.

The X-ray diagnostic apparatus according to the embodiment includes asupport frame and processing circuitry. The support frame supports anX-ray generator and an X-ray detector. The processing circuitry isconfigured to, when rotational acquisitions are performed multiple timesafter a contrast agent is injected one time, previously set a generationcondition of an X-ray that is generated by the X-ray generator for eachof the rotational acquisitions.

First Embodiment

FIG. 1 is a diagram that illustrates an example of the configuration ofan X-ray diagnostic apparatus 1 according to a first embodiment. Asillustrated in FIG. 1, the X-ray diagnostic apparatus 1 according to thefirst embodiment includes an X-ray acquisition mechanism 10 and an imageprocessing device 100. The X-ray acquisition mechanism 10 includes anX-ray generator 11, an X-ray detector (Flat Panel Detector (FPD)) 12, aC-shaped arm 13, and a bed 14, and it is connected to an injector 50.

The injector 50 is a device for injecting a contrast agent through acatheter that is inserted into a subject P. Here, there may be cases inwhich an injection of a contrast agent from the injector 50 is startedin accordance with an injection start command that is received via theimage processing device 100 that is described later or in accordancewith an injection start command that is directly input to the injector50 by an operator.

The C-shaped arm 13 supports the X-ray generator 11 and the X-raydetector 12, and it is rotated by a motor that is provided on a supportframe (not illustrated) at high speed like a propeller around thesubject P that lies on the bed 14. Here, the C-shaped arm 13 issupported such that it is rotatable with respect to the XYZ axes thatare the three axes that run at right angles to one another, and it isrotated by an undepicted driving unit with respect to each of the axesindividually. X-ray generator 11 is a device that includes an X-ray tubeand an X-ray movable diaphragm and generates X-rays through a highvoltage supplied from the X-ray high-voltage generating unit. The X-raytube applies X-rays. The X-ray movable diaphragm narrows the range ofthe X-rays applied from the X-ray tube to the subject P to a rangecontaining a region of interest of the subject P.

As illustrated in FIG. 1, the image processing device 100 includes anAnalog/Digital (A/D) conversion unit 21, an image memory 22, asubtraction unit 23, a filtering unit 24, an affine transformation unit25, a Look Up Table (LUT) 26, an acquisition control unit 27, ascattered-ray correction unit 28, a beam-hardening correction unit 29, aring correction unit 30, a three-dimensional reconstruction unit 31, athree-dimensional image processing unit 32, a control unit 33, and adisplay unit 40. Furthermore, although not illustrated, the imageprocessing device 100 includes an input unit, such as a mouse, keyboard,trackball, or pointing device, to receive various operations on theX-ray diagnostic apparatus 1 from an operator.

The display unit 40 displays various images that are processed by theimage processing device 100 or various types of information, such as aGraphical User Interface (GUI). For example, the display unit 40 is aCathode Ray Tube (CRT) monitor or a liquid crystal monitor. The A/Dconversion unit 21 is connected to the X-ray detector 12, and itconverts an analog signal input from the X-ray detector 12 into adigital signal and stores the converted digital signal as an X-rayacquisition image in the image memory 22. The image memory 22 stores theX-ray acquisition image (projection data). Furthermore, the image memory22 stores reconstruction data (volume data) that is reconstructed by thethree-dimensional reconstruction unit 31 that is described later orthree-dimensional images that are generated by the three-dimensionalimage processing unit 32.

The subtraction unit 23 generates a subtraction image, such as a DigitalSubtraction Angiography (DSA) image. For example, the subtraction unit23 generates a DSA image by using mask images and contrast images thatare stored in the image memory 22 or generates a three-dimensional bloodvessel image by using mask volume data that is reconstructed from maskimages and contrast volume data that is reconstructed from contrastimages. Here, under the control of the control unit 33 that is describedlater, the subtraction unit 23 generates a DSA image or athree-dimensional blood vessel image by using mask image and contrastimage.

The filtering unit 24 performs a high-pass filtering, a low-passfiltering, or the like. The affine transformation unit 25 makes anenlargement, minification, movement, or the like, of images. The LUT 26performs a tone conversion. The scattered-ray correction unit 28performs a scattered-ray correction to remove scattered ray componentsthat are included in a mask image and a contrast image. Thebeam-hardening correction unit 29 performs a beam hardening correctionby using a correction table on the basis of the thickness of softtissues, or the thickness of soft tissues and the thickness of a bonearea. The ring correction unit 30 performs a ring correction to removering-shaped artifacts due to the unevenness of gains of the X-raydetector 12, or the like.

Under the control of the control unit 33 that is described later, theacquisition control unit 27 controls various operations related toacquisition of the X-ray acquisition mechanism 10. For example, theacquisition control unit 27 controls rotational acquisition foracquiring projection data at a predetermined frame rate while theC-shaped arm 13 is rotated. For example, by using, as a trigger, asignal that is output at the start of an injection of a contrast agentfrom the injector 50, the acquisition control unit 27 controls multiplerotational acquisitions after a contrast agent is injected one time. Inother words, rotational acquisitions are automatically performedmultiple times after a contrast agent is injected once. Here, theacquisition control unit 27 controls the start of multiple rotationalacquisitions by using the elapsed time from a start of injection,thereby performing each rotational acquisition in synchronization withthe time in which a contrast agent reaches a target for the rotationalacquisition.

Furthermore, while the C-shaped arm 13 is controlled so as to rotate,the acquisition control unit 27 controls an undepicted high-voltagegenerating unit so as to generate X-rays continuously with the X-raygenerator 11 or intermittently and controls the X-ray detector 12 so asto detect X-rays that are transmitted through the subject P. Here, theacquisition control unit 27 generates X-rays on the basis of the X-raygeneration condition that is set for each rotational acquisition by thecontrol unit 33 that is described later.

The three-dimensional reconstruction unit 31 reconstructs reconstructiondata (volume data) from projection data that is acquired during arotational acquisition with the X-ray acquisition mechanism 10. Forexample, the three-dimensional reconstruction unit 31 reconstructsvolume data from post-subtraction projection data that is stored in theimage memory 22 after the subtraction unit 23 performs a subtraction ofmask images and corresponding contrast images. Alternatively, thethree-dimensional reconstruction unit 31 reconstructs mask and contrastvolume data from projection data that is stored in the image memory 22after the A/D conversion unit 21 performs a digital data conversion.Then, the three-dimensional reconstruction unit 31 stores thereconstructed volume data in the image memory 22.

The three-dimensional image processing unit 32 generates athree-dimensional image from volume data that is stored in the imagememory 22. For example, the three-dimensional image processing unit 32generates a volume rendering image or a Multi Planar Reconstruction(MPR) image from volume data. Then, the three-dimensional imageprocessing unit 32 stores the generated three-dimensional image in theimage memory 22.

The control unit 33 performs overall control of the X-ray diagnosticapparatus 1. Specifically, the control unit 33 controls variousoperations related to the acquisition of X-ray images by the X-rayacquisition mechanism 10, the generation of a various images, thedisplay of those images by the display unit 40, or the like. Forexample, the control unit 33 controls the rotational acquisition of theX-ray acquisition mechanism 10, the generation of a three-dimensionalimage from projection data that is acquired during the rotationalacquisition, and the display of rendering images on the display unit 40.Here, for example, as illustrated in FIG. 1, the control unit 33includes a condition setting unit 331, a correction control unit 332,and a display control unit 333, and it controls the X-ray generationcondition for each rotational acquisition, thereby enabling acquisitionof the optimum image data during each rotational acquisition.

As described above, in conventional X-ray diagnostic apparatuses, aftera contrast agent is injected, rotational acquisitions are performedmultiple times, and a three-dimensional image is generated fromprojection data that is acquired during each rotational acquisition,whereby it is possible to reduce patients' invasiveness during imaging.However, in conventional X-ray diagnostic apparatuses, after a contrastagent is injected, multiple rotational acquisitions are performed byusing the same X-ray generation condition; therefore, it is sometimesdifficult to acquire the optimum image data during each rotationalacquisition.

For example, when rotational acquisitions are performed twice after acontrast agent is injected once, if a contrast agent signal that isacquired during the second acquisition is extremely weaker than acontrast agent signal that is acquired during the first acquisition, andif the second acquisition is performed with the same condition of thefirst acquisition, the dose during the second acquisition isinsufficient; therefore, it is difficult to separate noise and signals,and it is difficult to correctly observe the object of interest.Furthermore, for example, when rotational acquisitions are performedtwice after a contrast agent is injected once, if detailed structure isrequired at the first acquisition while broad structure is required atthe second acquisition, and if the second acquisition is performed withthe same condition of the first acquisition, the dose during the secondacquisition is excessive.

Therefore, in the X-ray diagnostic apparatus 1 according to the presentembodiment, the above-described control unit 33 controls the X-raygeneration condition for each rotational acquisition so that it ispossible to acquire the optimum image data during each rotationalacquisition. Specifically, if rotational acquisitions are performedmultiple times after a contrast agent is injected once, the conditionsetting unit 331 previously sets, for each rotational acquisition, thegeneration condition of X-rays that are generated by the X-ray generator11. For example, the condition setting unit 331 previously sets at leastone of the tube voltage, the tube current, the pulse width, the X-raytube focus size, and the beam filter as the X-ray generation conditionfor each rotational acquisition.

The correction control unit 332 corrects data that is acquired by theX-ray detector 12 in accordance with the X-ray generation condition thatis set by the condition setting unit 331. Specifically, if a subtractionoperation is performed by using mask images and corresponding contrastimages that are acquired under the different generation conditions, thecorrection control unit 332 corrects the projection data such that thesubtraction operation is performed on the sets of projection data forwhich the generation conditions are matched.

The display control unit 333 controls the display unit 40 to displaymultiple rendering images created from multiple three-dimensional imagesthat are taken during rotational acquisitions under the X-ray generationconditions that are set by the condition setting unit 331.

An explanation is given below, with reference to FIG. 2, of an exampleof the operation of the X-ray diagnostic apparatus 1 according to thepresent embodiment. FIG. 2 is a flowchart that illustrates an example ofthe steps of the operation of the X-ray diagnostic apparatus 1 accordingto the first embodiment. Furthermore, FIG. 2 illustrates a case where,before a contrast agent is injected, a rotational acquisition isperformed for mask images and, after the contrast agent is injected,rotational acquisitions are performed twice.

As illustrated in FIG. 2, in the X-ray diagnostic apparatus 1, before acontrast agent is injected, mask images are acquired during a rotationalacquisition at first (Step S101). Specifically, in the X-ray diagnosticapparatus 1, the acquisition control unit 27 controls the X-rayacquisition mechanism 10 so as to acquire projection data at apredetermined frame with the X-ray generation conditions that are set bythe condition setting unit 331. Furthermore, projection data for maskimages are converted into digital signals by the A/D conversion unit 21and is stored in the image memory 22.

After acquisition of mask images are completed, the injector 50 injectsa contrast agent into the subject P (Step S102). After the contrastagent is injected, and after a predetermined time (a first elapsed time)elapses, the acquisition control unit 27 acquires the first contrastimages by a rotational acquisition with the X-ray generation conditionsthat are set by the condition setting unit 331 (Step S103). Here, thecondition setting unit 331 changes the X-ray generation conditions foracquiring the second contrast images (Step S104).

Then, after the second elapsed time that is longer than the firstelapsed time elapses after the contrast agent is injected, theacquisition control unit 27 acquires the second contrast images during arotational acquisition with the X-ray generation conditions that arechanged by the condition setting unit 331 (Step S105). Here, thecondition setting unit 331 changes at least one of the tube voltage, thetube current, the pulse width, the X-ray tube focus size, and the beamfilter as the X-ray generation conditions for each rotationalacquisition. FIG. 3 is a diagram that illustrates an example of therotational acquisition of the X-ray diagnostic apparatus 1 according tothe first embodiment. Here, FIG. 3 illustrates, for example, a casewhere the mask images and the first contrast images are acquired underthe same X-ray generation condition and the pulse width of X-rays thatare generated by the X-ray generator 11 is changed for the secondcontrast images.

For example, in the X-ray diagnostic apparatus 1, as illustrated in FIG.3, during the mask image acquisition that is equivalent to Step S101 ofFIG. 2, the C-shaped arm 13 is rotated (forward) at 60 degrees persecond (arm rotation speed: 60°/sec), while the projections are acquiredat fixed frame rate (frame rate: 60 fps), and the mask image of 200frames is gotten at an interval of 1 degree. Here, the condition settingunit 331 sets the X-ray generation condition “the tube voltage: 100 kV”,“the tube current: 250 mA”, “the pulse width: 12 msec”, “the tube focussize: Focus Middle (0.6 mm)”, and “the beam filter: Al 1.8 mm”. Theacquisition control unit 27 causes the mask image of 200 frames to beacquired under the above-described X-ray generation condition that isset by the condition setting unit 331. The acquired mask image of 200frames is converted into digital signals by the A/D conversion unit 21and is stored in the image memory 22.

After the mask image is acquired, the C-shaped arm 13 is returned(rotated backward) to the initial rotation start position at high speed60 degrees per second. Next, a contrast agent is injected by theinjector 50 and, after a certain period of time elapses, during thefirst contrast image acquisition that is equivalent to Step S103 of FIG.2, the C-shaped arm 13 is rotated (forward) at 60 degrees per second(arm rotation: 60°/sec), the projections are acquired at a fixed framerate (frame rate: 60 fps), and the first contrast image of 200 frames isgotten at an interval of 1 degree. Here, the condition setting unit 331sets the same X-ray generation condition with that for the mask imageacquisition. Specifically, the acquisition control unit 27 causes thefirst contrast image of 200 frames to be acquired with “the tubevoltage: 100 kV”, “the tube current: 250 mA”, “the pulse width: 12msec”, “the tube focus size: Focus Middle (0.6 mm)”, and “the beamfilter: Al 1.8 mm”. The acquired first contrast image of 200 frames isconverted into digital signals by the A/D conversion unit 21 and isstored in the image memory 22.

After the first contrast image is acquired, and after a specific time(the time that is different from the first time) elapses after the startof imaging, during the second contrast image acquisition that isequivalent to Step S105 of FIG. 2, the C-shaped arm 13 is rotated(backward) at 60 degrees per second (arm rotation: 60°/sec), theprojections are acquired at a fixed frame rate (frame rate: 60 fps), andthe second contrast image of 200 frames is gotten at an interval of 1degree. Here, the condition setting unit 331 changes the X-raygeneration condition for acquiring the second contrast image (anequivalent of Step S104 of FIG. 2). For example, the condition settingunit 331 changes “the pulse width” from “12 msec” to “6 msec” foracquiring the second contrast image. Specifically, the acquisitioncontrol unit 27 causes the second contrast image of 200 frames to beacquired with “the tube voltage: 100 kV”, “the tube current: 250 mA”,“the pulse width: 6 msec”, “the tube focus size: Focus Middle (0.6 mm)”,and “the beam filter: Al 1.8 mm”. Specifically, the condition settingunit 331 sets the X-ray generation condition such that, out of therotational acquisitions that are performed multiple times, the totalamount of X-ray radiation during the second rotational acquisition,which is performed after the first rotational acquisition, is nearlyequal to or less than ½ of the total amount of X-ray radiation duringthe first rotational acquisition. The acquired second contrast image of200 frames is converted into digital signals by the A/D conversion unit21 and is stored in the image memory 22.

As described above, the X-ray diagnostic apparatus 1 acquires the firstcontrast image and the second contrast image for which, for example, the“pulse width” is changed. With reference back to FIG. 2, after thesecond contrast image is acquired at Step S105, the subtraction unit 23performs a subtraction on the first contrast image and the secondcontrast image for which a correction has been performed in accordancewith the X-ray generation condition under the control of the correctioncontrol unit 332 (Step S106). Here, if a subtraction operation isperformed on projection data on the mask image and projection data onthe contrast image that are acquired under the different generationconditions, the correction control unit 332 corrects the projection datasuch that the subtraction operation is performed on the sets ofprojection data for which the generation conditions are matched.

For example, the correction control unit 332 causes a subtractionoperation to be performed on the mask image and the first contrast imagethat are acquired under the X-ray generation conditions illustrated inFIG. 3 by using the following Equation (1) and causes a subtractionoperation to be performed on the mask image and the second contrastimage that are acquired under the X-ray generation condition illustratedin FIG. 3 by using the following Equation (2). Here, DSA_(θ)(x, y),MASK_(θ)(x, y), CONT1_(θ)( )(x, y), and CONT2_(θ)(x, y) in Equation (1)and Equation (2) represent subtraction data, the mask image, the firstcontrast image, and the second contrast image. Furthermore, “θ” inEquation (1) and Equation (2) represents the rotation angle.

$\begin{matrix}{{{DSA}_{\theta}\left( {x,y} \right)} = {\log_{e}\left( {- \frac{{CONT}\; 1_{\theta}\left( {x,y} \right)}{{MASK}_{\theta}\left( {x,y} \right)}} \right)}} & (1) \\{{{DSA}_{\theta}\left( {x,y} \right)} = {\log_{e}\left( {- \frac{2 \times {CONT}\; 2_{\theta}\left( {x,y} \right)}{{MASK}_{\theta}\left( {x,y} \right)}} \right)}} & (2)\end{matrix}$

For example, if a subtraction operation is performed on the mask imageand the first contrast image for which the X-ray generation conditionsare the same, the subtraction operation is performed without acorrection by the correction control unit 332. Specifically, asrepresented by Equation (1), the subtraction unit 23 reads, from theimage memory 22, the mask image of 200 frames and the first contrastimage of 200 frames and performs a subtraction (Log subtraction) byusing projection data of the corresponding rotation angle, therebygenerating subtraction data for the first contrast image.

Furthermore, if a subtraction operation is performed on the mask imageand the second contrast image for which the X-ray generation conditionsare different, the subtraction operation is performed after thecorrection control unit 332 performs a correction. For example, asillustrated in FIG. 3, if a subtraction is performed on the mask imagethat is acquired with “the pulse width: 12 msec” and the second contrastimage that is acquired with “the pulse width: 6 msec”, the subtractionunit 23 generates subtraction data for the second contrast image byusing the equation in which the second contrast image is multiplied bythe correction factor “2” as represented by Equation (2). Specifically,the subtraction unit 23 reads, from the image memory 22, the mask imageof 200 frames and the second contrast image of 200 frames and performs asubtraction by using projection data of the corresponding rotation angleby using Equation (2), thereby generating subtraction data for thesecond contrast image.

As described above, with regard to a change in the tube current and thepulse width for which the amount of X-rays is linearly changed, thecorrection control unit 332 controls the subtraction unit 23 so as todetermine a correction factor to compensate for the change and perform asubtraction using the determined correction factor. Furthermore, anexplanation is given in FIG. 2 of a case where a subtraction isperformed after the second contrast image is acquired; however, there isno limitation on the embodiment and, for example, there may be a casewhere subtraction data on the first contrast image is generated whilethe second contrast image is acquired.

After sets of subtraction data on the first contrast image and thesecond contrast image are generated at Step S106, each set ofsubtraction data is transmitted to the three-dimensional reconstructionunit 31 so that volume data is generated. Specifically, thethree-dimensional reconstruction unit 31 reconstructs volume data fromeach set of data on which a subtraction has been performed (Step S107).For example, the three-dimensional reconstruction unit 31 reconstructsvolume data by using a filtered backprojection method that is proposedby Feldkamp et al.

In such a case, the three-dimensional reconstruction unit 31 applies anappropriate convolution filter of Shepp & Logan, Ramachandran, or thelike, to subtraction data for the first contrast image and then performsa back projection calculation, thereby reconstructing volume data.Furthermore, as the area of interest in the second contrast image doesnot need much high spatial resolution, the three-dimensionalreconstruction unit 31 applies, to the subtraction data for the secondcontrast image, for example, a convolution filter that has a furtherweaker spatial enhancement compared to the filter that is used for thereconstruction of the first contrast image and then performs a backprojection calculation, thereby reconstructing volume data.

Here, a reconstruction area is defined as a cylinder that is inscribedin a bundle of X-rays from the X-ray generator 11 in all directionsduring rotational acquisition. For example, the inside of the cylinderis made discrete in three dimensions by the length “d” at the centralportion of a reconstruction area that is projected onto the width of asingle detection element of the X-ray detector 12, and a reconstructionimage is obtained from data on the discrete points. Furthermore,although an example of the discrete interval is illustrated here, thisis sometimes different depending on apparatuses and manufacturers;therefore, basically, it is appropriate to use the discrete intervalthat is defined by the apparatus. Moreover, there may be a case where areconstruction is performed by using iterative reconstructionalgorithms, such as an Algebraic Reconstruction Algorithm (ART) method,an Expectation Maximization (EM) method, or a Total Variation (TV)method. The volume data that is reconstructed by the three-dimensionalreconstruction unit 31 as described above is stored in the image memory22.

After the volume data is reconstructed at Step S107, thethree-dimensional image processing unit 32 generates rendering imagesfrom the reconstructed volume data, and the display control unit 333displays the generated rendering images on the display unit 40 (StepS108). For example, the three-dimensional image processing unit 32generates volume rendering images or MPR images from volume data asdescribed above. Here, the display control unit 333 fuses generatedvolume rendering images or MPR images for a display, or displaysrendering images in different colors.

An explanation is given above of an example of the operation performedby the X-ray diagnostic apparatus 1 according to the first embodiment.In the above-described example, an explanation is given of a case wherethe pulse width for acquiring the second contrast image is shorter thanthe pulse width for acquiring the first contrast image so that theamount of X-rays for the second contrast image is smaller than that forthe first contrast image. This embodiment is applied to acquisitions of,for example, hepatic arteries, portal veins, or arteries of the brain.For example, proper hepatic arteries, portal veins, internal carotidarteries, vertebral arteries, or the like, are acquired with the firstcontrast image, and corona enhancement, hepatic veins, veins of thebrain, capillary blood vessels, or the like, are acquired with thesecond contrast image. In such a case, if a rotational acquisition isperformed on an arterial phase of the subject P, the condition settingunit 331 sets the X-ray generation conditions such that the amount ofX-rays is increased compared to the other phases and, if a rotationalacquisition is performed on a capillary blood vessel phase or a venousphase of the subject P, it sets the X-ray generation condition such thatthe amount of X-rays is decreased compared to the other phases.

The X-ray diagnostic apparatus 1 conducts rotational acquisitionsmultiple times as described above so that it can acquire the optimumimage data during each rotational acquisition. For example, if region ofinterest for the first acquisition has a detailed structure while regionof interest for the second acquisition has a broad structure, the X-raydiagnostic apparatus 1 can prevent an unnecessary increase in theexposed dose due to the overmuch dose during the second acquisition andcan provide the optimum image for an observation. For example, thisembodiment is applied to acquisition in the case of an identification ofa feeding artery for supplying nutrients and oxygen to a tumor inaddition to an identification of a tumor. For example, as illustrated inFIG. 4, the X-ray diagnostic apparatus 1 can visualize a narrow artery(feeding artery) that is newly grown in accordance with the formation ofa tumor as the first contrast image, visualize a vein as the secondcontrast image, and then fuse them to obtain a colored display image ofdifferent colors (e.g., coloring of an artery in red, a vein in blue, orthe like), and display it on the display unit 40 as an easily observedimage. Thus, for example, it is possible to operate a catheter on thebasis of the information on a feeding artery. Furthermore, FIG. 4 is adiagram that illustrates an example of a display image according to thefirst embodiment.

Furthermore, this embodiment is applied to visualizing for identifying adisease site in detail when there is disease, such as an aneurysm, inarteries of the brain, or the like. For example, it is applicable tobrain surgery for cerebral aneurysm or an arteriovenous malformationthat is a connection between arteries and veins via a nidus. Morespecifically, when brain surgery is conducted, it is often consideredthat the information on an artery that is the therapeutic objective isall that is needed. However, when brain surgery is conducted, it isdesirable that the area of removed skull is smaller. Here, if veins areoverlapped in the surgery site where the amount of removed skull issmall, there is a need to find another approach so as to prevent damagesto the veins, which results in an increase in the burden on a patient.Therefore, for brain surgery, arteries and veins are sometimes capturedto avoid previous potential risks. In such a case, the condition settingunit 331 makes, for example, the pulse width for acquiring a vein as thesecond contrast image narrower than the pulse width for acquiring anartery as the first contrast image.

Furthermore, this embodiment is applicable to a case where, for example,if there is a need to determine whether there is no infarct, an arteryis visualized as the first contrast image and a capillary blood vesselis visualized as the second contrast image. In such a case, thecondition setting unit 331 makes, for example, the pulse width foracquiring a capillary blood vessel as the second contrast image narrowerthan the pulse width for acquiring an artery as the first contrastimage.

Modified Example 1

In the above-described embodiment, an explanation is given of a casewhere the amount of X-rays for the second contrast image is smaller thanthat for the first contrast image; however, there is no limitation onthe embodiment, and there may be a case where the amount of X-rays forthe second contrast image is larger than that for the first contrastimage. For example, if the detailed blood vessel structure, or the like,is unnecessary for arteries and it is only necessary to know the roughblood vessel structure, the amount of X-rays is reduced to preventunnecessary radiation exposure. However, the density of a contrast agentin capillary blood vessels or veins is lower than that in arteries;therefore, if capillary blood vessels or veins with low contrast agentsignals need to be displayed with a certain spatial resolution in spiteof noise (if there is a need for an observation in more detail comparedto a spatial resolution for capillary blood vessels or veins although itis slightly poorer spatial resolution for arteries in theabove-described example), the amount of X-rays for the second contrastimage is made larger than that for the first contrast image. Forexample, the modified example 1 is applied to acquisition such asCT-like imaging that is performed during hepatic arteriography in thecase of a diagnosis for a hepatocellular tumor. During the acquisitionof an earlier phase in a CT-like imaging, a hepatocellular tumor ishighly contrasted, and therefore a hepatocellular tumor can beidentified with a small amount of X-rays. Thus, the condition settingunit 331 reduces the amount of X-rays during the acquisition of anearlier phase in a CT-like imaging. Conversely, during the acquisitionof a later phase in a CT-like imaging, an image (corona enhancement) ofa contrast agent remained at around a hepatocellular tumor is observed.With regard to the corona enhancement, the contrast is weaker comparedto the enhancement of hepatocellular tumor at earlier phase. Therefore,the condition setting unit 331 sets a larger amount of X-rays during theacquisition of a later phase compared to the acquisition of an earlierphase. Furthermore, the corona enhancement is not observed for otherthan hepatocellular tumors and, if this enhancement is observed, ahepatocellular tumor is suggested with higher percentage.

Furthermore, the above-described modified example 1 is also applied toan acquisition during a treatment for which reference information isobtained with regard to an arterial phase in which a catheter is justpassed through after the catheter is inserted through a vein. In such acase, the condition setting unit 331 sets a larger amount of X-rays foracquiring a venous phase as the second contrast image compared to thatfor acquiring an arterial phase as the first contrast image.

In such a case, for example, contrary to the above-described case, thefirst contrast image is acquired with “the tube voltage: 100 kV”, “thetube current: 250 mA”, “the pulse width: 6 msec”, “the tube focus size:Focus Middle (0.6 mm)”, and “the beam filter: Al 1.8 mm”, and the secondcontrast image is acquired with “the tube voltage: 100 kV”, “the tubecurrent: 250 mA”, “the pulse width: 12 msec”, “the tube focus size:Focus Middle (0.6 mm)”, and “the beam filter: Al 1.8 mm”. Specifically,the condition setting unit 331 sets the X-ray generation condition suchthat, with regard to the rotational acquisitions that are performedmultiple times, the total amount of X-ray radiation during the secondrotational acquisition, which is performed after the first rotationalacquisition, is nearly equal to or more than twice the total amount ofX-ray radiation during the first rotational acquisition. Furthermore, inthis case, the correction factor “2” for the X-ray generation conditiondifference is inserted into Equation (1), and the correction factor “2”is removed from Equation (2).

Modified Example 2

Furthermore, in the above-described embodiment, an explanation is givenof a case where a subtraction image is reconstructed. However, there isno limitation on the embodiment and, for example, there may be a casewhere a subtraction is performed after reconstruction. In such a case,if a subtraction operation is performed on sets of reconstruction datathat is reconstructed from sets of projection data such as a mask imageand contrast images that are acquired under different generationconditions, the correction control unit 332 corrects the reconstructiondata such that the subtraction operation is performed by using the setsof reconstruction data for which the generation conditions are matched.

For example, the three-dimensional reconstruction unit 31 readsprojection data of the mask image, the first contrast image, and thesecond contrast image from the image memory 22 and reconstructs volumedata individually. Then, the subtraction unit 23 performs a subtractionof reconstructed volume data reconstructed from the mask image and eachof the contrast images. Here, the subtraction unit 23 performs asubtraction by using data that is corrected by using a correction factorthat is determined by the correction control unit 332.

As described above, as a subtraction is performed after reconstruction,artifacts due to misregistration can be removed. For example, if therotation direction of the C-shaped arm 13 for acquiring a mask image isdifferent from the rotation direction of the C-shaped arm 13 foracquiring a contrast image, there is a possibility of the occurrence ofmisregistration at an edge portion even with the same angle due to thedifference in the rotation direction. Therefore, a reconstruction isfirst performed so that the positional deviation during acquisitions iscorrected for each rotational acquisition, and artifacts due tomisregistration are removed.

Modified Example 3

Furthermore, in the above-described embodiment, an explanation is givenof a case where the mask image is acquired and a subtraction isperformed by using the first contrast image and the second contrastimage. However, there is no limitation on the embodiment, and there maybe a case where the mask image is not acquired but only the firstcontrast image and the second contrast image are acquired. In such acase, the density of a contrast agent is changed or various correctionoperations are performed in accordance with a purpose. For example, ifonly blood vessels are interested in the density of a contrast agent isincreased, and the first contrast image and the second contrast imageare acquired with respect to blood vessels that are imaged at differenttimings after the contrast agent is injected. In this case, signals dueto a contrast agent are strong; therefore, there may be a case where ascattered-ray correction, or the like, for removing scattered rays isnot performed.

Furthermore, for example, if both blood vessels and soft tissues areinterested in, a low-density contrast agent is injected to preventartifacts come from strong signals for soft tissues observation, and thefirst contrast image and the second contrast image are acquired. In thiscase, as signals due to a contrast agent are weak, a scattered-raycorrection, a subtraction for a correction image for correcting densitynon-uniformity, and a beam hardening correction are performed on thefirst contrast image and the second contrast image. Afterward, thethree-dimensional reconstruction unit 31 performs reconstruction ofvolume data. Furthermore, there may be a case where a ring correction isperformed in addition to the above-described corrections.

Modified Example 4

Furthermore, in the above-described embodiment, an explanation is givenof a case where images are acquired with the same tube focus size.However, there is no limitation on the embodiment, and there may be acase where the tube focus size is changed. For example, if acquisitionis performed under the X-ray generation condition in which the amount ofX-rays is small, a relative noise level is increased; however, if thetarget is a vein, or the like, lower spatial resolution may beacceptable and, if a reconstruction is performed by using a filter witha low degree of spatial enhancement, a smooth image with reduced noiseis generated. Here, if the tube focus size is increased, an imagebecomes blurred, and noise is relatively reduced; therefore, it ispossible to obtain the same effect as that of a reconstruction using afilter with a low degree of spatial enhancement. For example, the sameeffect is expected in a case where the image acquired with the tubefocus size “0.6 mm” is reconstructed by using a filter with a low degreeof spatial enhancement and in a case where the image acquired with thetube focus size “1.0 mm” is reconstructed by using a filter with a highdegree of spatial enhancement. Therefore, for example, if the secondcontrast image is acquired under the X-ray generation condition in whichthe amount of X-rays is small, the correction control unit 332 canperform a control so as to generate a smooth image by simultaneouslyincreasing the tube focus size.

Modified Example 5

Furthermore, in the above-described embodiment, an explanation is givenof a case where images are acquired with the same tube voltage and beamfilter. However, there is no limitation on the embodiment, and there maybe a case where the tube voltage or the beam filter is changed. Here, ifthe tube voltage or the beam filter is changed, the radiation quality ofX-rays is changed; therefore, instead of the above-described linearcorrection, a correction is performed by using correction data with allthe combinations before and after a change for each region.Specifically, if at least one of the tube voltage and the beam filter isdifferent during multiple rotational acquisitions, the correctioncontrol unit 332 corrects difference between sets of data due todifferent beam quality.

An explanation is given below, with reference to FIGS. 5 to 7, ofcorrection data if the tube voltage or the beam filter is changed. FIG.5 is a diagram that illustrates an example of an acquiring by usingcorrection data according to a modified example 5. For example, asillustrated in FIG. 5, the mask image and the first contrast image ofthe 200 frames are acquired with “the tube voltage: 100 kV”, “the tubecurrent: 250 mA”, “the pulse width: 12 msec”, “the tube focus size:Focus Middle (0.6 mm)”, and “the beam filter: Cu 0.2 mm”. Conversely,with regard to the second contrast image, the tube voltage and the beamfilter are changed, and the second contrast image of 200 frames isacquired with “the tube voltage: 80 kV”, “the tube current: 250 mA”,“the pulse width: 12 msec”, “the tube focus size: Focus Middle (0.6mm)”, and “the beam filter: Al 1.8 mm”.

In such a case, the beam quality of X-rays is changed, and the degree oftransmission to an object is changed; therefore, instead of a simplelinear correction, a correction is performed by using correction datathat is generated as illustrated in FIGS. 6 and 7, for example. FIG. 6is a diagram that illustrates an example of generation of correctiondata according to the modified example 5. For example, with regard tocorrection data according to the modified example 5, projection data isfirst acquired by using the tube voltage and the beam filter before andafter a change, as illustrated in FIG. 6. Specifically, as illustratedin (a) of FIG. 6, the projection data “A_(θ=0(100, 0.2))(x, y)” in astate where nothing is placed and the projection data“Fe_(θ=0(100, 0.2))(x, y)” in a state where a phantom is placed areacquired under the condition of “the tube voltage: 100 kV” and “the beamfilter: Cu 0.2 mm”. Here, each set of the above-described projectiondata is acquired while the rotation angle “θ” is changed. Thus,projection data for the transmission through various thicknesses isacquired.

In the same manner, as illustrated in (β) of FIG. 6, the projection data“A_(θ=0(80, 1.8))(x, y)” in a state where nothing is placed and theprojection data “F_(θ=0(80, 1.8))(x, y)” in a state where a phantom isplaced are acquired under the condition of “the tube voltage: 80 kV” and“the beam filter: Al 1.8 mm”. Here, each set of the above-describedprojection data is also acquired while the rotation angle “0” ischanged. To generate correction data, a subtraction is performed byusing the following Equation (3) and Equation (4) on the projection datathat is acquired with each beam quality as described above, and thevalues of subtraction data are derived. Here, “α” in Equation (3)represents subtraction data under the condition of “the tube voltage:100 kV” and “the beam filter: Cu 0.2 mm”. Furthermore, “β” in Equation(4) represents subtraction data under the condition of “the tubevoltage: 80 kV” and “the beam filter: Al 1.8 mm”.

$\begin{matrix}{\alpha = {\log_{e}\frac{F_{\theta = {0{({100,0.2})}}}\left( {x,y} \right)}{A_{\theta = {0{({100,0.2})}}}\left( {x,y} \right)}}} & (3) \\{\beta = {\log_{e}\frac{F_{\theta = {0{({80,1.8})}}}\left( {x,y} \right)}{A_{\theta = {0{({80,1.8})}}}\left( {x,y} \right)}}} & (4)\end{matrix}$

Specifically, to generate correction data, as represented by Equation(3) and Equation (4), subtraction data is calculated with respect toeach projection angle. Then, to generate correction data, as illustratedin FIG. 7, for example, correction data is generated, in which sets ofsubtraction data with each beam quality at the same position arerelated. FIG. 7 is a diagram that illustrates an example of correctiondata according to the modified example 5.

For example, as illustrated in the upper section of FIG. 7, correctiondata is generated as a graph in which the vertical axis represents “α”,the horizontal axis represents “β”, and subtraction data of eachposition is plotted. Furthermore, the correction data is generated as agraph L1 that is formed by a plural-degree expression by using aleast-square method based on the plotted data and, furthermore, a graphL2 is generated which is normalized by using the values of thehorizontal axis “P” as illustrated in the lower section of FIG. 7.

For correction data, the graph illustrated in FIG. 7 is generated withall the combinations before and after a change in the beam quality and,furthermore, the graph with all the combinations is generated for eachregion, such as a chest, abdomen, neck, or pelvic region. Furthermore,in FIG. 6, an explanation is given of a case where the correction datais generated by using a phantom; however, there is no limitation on theembodiment and, for example, there may be a case where it is generatedby acquiring projection data while the thickness is gradually changed byusing an acrylic board, or the like. Furthermore, there may be a casewhere a large number of standard CT images are prepared for each regionand correction data is generated by simulation.

The correction control unit 332 according to the modified example 5performs a control so that a correction is performed by using correctiondata that is generated as described above. For example, if rotationalacquisitions are performed under the conditions illustrated in FIG. 5,the correction control unit 332 causes a subtraction operation to beperformed on the mask image and the second contrast image that areacquired under the X-ray generation conditions illustrated in FIG. 5 byusing the following Equation (5). Here, DSA_(θ)(x, y), MASK_(θ)(x, y),and CONT2_(θ)(x, y) in Equation (5) represent subtraction data, the maskimage, and the second contrast image. Furthermore, “θ” in Equation (5)represents the rotation angle. Moreover, “q” in Equation (5) is acorrection factor that is determined from correction data.

$\begin{matrix}{{{DSA}_{\theta}\left( {x,y} \right)} = {\log_{e}\left( {- \frac{q^{*}{CONT}\; 2_{\theta}\left( {x,y} \right)}{{MASK}_{\theta}\left( {x,y} \right)}} \right)}} & (5)\end{matrix}$

For example, if a subtraction operation is performed on a mask image anda contrast image for which at least one of the tube voltage and the beamfilter is different, the subtraction operation is performed after thecorrection control unit 332 performs a correction. For example, asrepresented by Equation (5), the subtraction unit 23 generatessubtraction data on the second contrast image by using the equation inwhich the second contrast image is multiplied by the correction factor“q”. Here, the correction control unit 332 calculates the average valuefrom the correction data with respect to each acquisition direction anduses the calculated average value as the correction factor “q”.

Here, there may be a case where the correction factor “q” is determinedon a pixel by pixel basis. Specifically, the correction control unit 332corrects the difference between sets of data due to beam quality on apixel by pixel basis. In such a case, correction data is generated foreach pixel, and the correction control unit 332 performs a control suchthat a correction is performed by using the generated correction datafor each pixel. For example, if rotational acquisitions are performedunder the conditions illustrated in FIG. 5, the correction control unit332 causes a subtraction operation to be performed on the mask image andthe second contrast image that are acquired under the X-ray generationconditions illustrated in FIG. 5 by using the following Equation (6).

$\begin{matrix}{{{DSA}_{\theta}\left( {x,y} \right)} = {\log_{e}\left( {- \frac{{q\left( {x,y} \right)}^{*}{CONT}\; 2_{\theta}\left( {x,y} \right)}{{MASK}_{\theta}\left( {x,y} \right)}} \right)}} & (6)\end{matrix}$

Specifically, the subtraction unit 23 generates subtraction data on thesecond contrast image by using the equation in which the second contrastimage is multiplied by the correction factor “q(x, y)” on a pixel bypixel basis, as represented by Equation (6).

Furthermore, in the above-described modified example 5, an explanationis given of a case where a correction is performed on projection data;however, there is no limitation on the embodiment, and there may be acase where a correction is performed on reconstructed volume data. Insuch a case, correction data on volume data is generated in the samemanner as the correction data on projection data. Specifically, areconstruction voxel value with regard to each beam quality is plottedon a graph as illustrated in FIG. 7, a graph is generated which isformed by a plural-degree expression by using a least-square methodbased on the plotted data, and correction data is generated which isnormalized by using the values of the horizontal axis. In the samemanner, correction data is generated with respect to all thecombinations of the beam qualities. Furthermore, correction data is alsogenerated for each region, such as a chest, abdomen, neck, or pelvicregion.

In the above-described first embodiment and the modified examples 1 to5, an explanation is given of a case where at least one of the tubevoltage, the tube current, the pulse width, the X-ray tube focus size,and the beam filter is set for each rotational acquisition. Here, theX-ray generation condition for each rotational acquisition may bepreviously determined for each acquisition sequence during whichmultiple rotational acquisitions are performed, or there may be a casewhere it is set by an operator at the time of acquisition.

As described above, according to the first embodiment, the C-shaped arm13 supports the X-ray generator 11 and the X-ray detector 12. Ifrotational acquisitions, which are acquisitions while the C-shaped arm13 is rotated, are performed multiple times after a contrast agent isinjected one time, the condition setting unit 331 sets the generationcondition of X-rays that are generated by the X-ray generator 11 foreach rotational acquisition. Therefore, the X-ray diagnostic apparatus 1according to the first embodiment can change the X-ray generationcondition for each rotational acquisition and can acquire the optimumimage data during each rotational acquisition.

For example, when rotational acquisitions are performed twice after acontrast agent is injected, if a signal acquired during the secondacquisition is extremely weaker than a signal acquired during the firstacquisition, the X-ray diagnostic apparatus 1 increases the amount ofX-rays during the second acquisition; thus, it is possible to eliminatea shortage of the dose and to provide an image by which the object ofinterest can be correctly observed. Furthermore, for example, whenrotational acquisitions are performed twice after a contrast agent isinjected, if the region of interest during the first acquisition has adetailed structure while the region of interest during the secondacquisition has a rough structure, the X-ray diagnostic apparatus 1reduces the amount of X-rays during the second acquisition; thus, it ispossible to prevent an unnecessary dose and to provide an image by whichthe object of interest can be correctly observed.

Furthermore, according to the first embodiment, the condition settingunit 331 sets, for each rotational acquisition, at least one of the tubevoltage, the tube current, the pulse width, the X-ray tube focus size,and the beam filter as the X-ray generation condition. Therefore, theX-ray diagnostic apparatus 1 according to the first embodiment canchange the details of the X-ray generation condition for each rotationalacquisition.

Furthermore, according to the first embodiment, the correction controlunit 332 corrects data that is acquired by the X-ray detector 12 inaccordance with the X-ray generation condition that is set by thecondition setting unit 331. Therefore, the X-ray diagnostic apparatus 1according to the first embodiment can display the accurate displayimage.

Furthermore, according to the first embodiment, if a subtractionoperation is performed by using a mask image and a contrast image thatare acquired under different generation conditions, the correctioncontrol unit 332 corrects those projection data such that thesubtraction operation is performed on the sets of projection data forwhich the generation conditions are matched. In other words, when asubtraction operation is performed by using projection data of a maskimage and projection data of a contrast image that are acquired underdifferent generation conditions, the correction control unit 332corrects at least one of the projection data of the mask image and theprojection data of the contrast image such that the subtractionoperation is performed by using sets of projection data for which thegeneration conditions are matched. Therefore, the X-ray diagnosticapparatus 1 according to the first embodiment can properly perform acorrection.

Furthermore, according to the first embodiment, if a subtractionoperation is performed by using reconstruction data that arereconstructed from a mask image and a contrast image that are acquiredunder different generation conditions, the correction control unit 332corrects the reconstruction data such that the subtraction operation isperformed on the sets of reconstruction data for which the generationconditions are matched. In other words, when a subtraction operation isperformed by using reconstruction data that is reconstructed fromprojection data of a mask image and reconstruction data that isreconstructed from projection data of a contrast image that are acquiredunder different generation conditions, the correction control unit 332corrects at least one of the reconstruction data that is reconstructedfrom the projection data of the mask image and the reconstruction datathat is reconstructed from the projection data of the contrast imagesuch that the subtraction operation is performed by using sets ofreconstruction data for which the generation conditions are matched.Therefore, the X-ray diagnostic apparatus 1 according to the firstembodiment can remove artifacts due to misregistration.

Furthermore, according to the first embodiment, if there is a differencein at least one of the tube voltage and the beam filter during multiplerotational acquisitions, the correction control unit 332 corrects thedifference between sets of data due to different beam quality.Therefore, the X-ray diagnostic apparatus 1 according to the firstembodiment can handle with a change in the X-ray generation condition bywhich the beam quality is changed.

Furthermore, according to the first embodiment, the correction controlunit 332 corrects the difference between sets of data due to the degreeof hardness on a pixel by pixel basis. Therefore, the X-ray diagnosticapparatus 1 according to the first embodiment can perform a correctionwith higher accuracy.

Furthermore, according to the first embodiment, the display control unit333 causes the display unit 40 to display multiple three-dimensionalimages that are taken during rotational acquisitions under the X-raygeneration conditions that are set by the condition setting unit 331.Therefore, the X-ray diagnostic apparatus 1 according to the firstembodiment can display an easily observable image with regard to theimages taken during multiple rotational acquisitions.

Furthermore, according to the first embodiment, the display control unit333 fuses multiple three-dimensional images for a display. Therefore,the X-ray diagnostic apparatus 1 according to the first embodiment makesit possible to instantly check the positional relationship between theobjects that are captured during different time phases.

Furthermore, according to the first embodiment, the display control unit333 causes multiple three-dimensional images to be displayed indifferent colors. Therefore, the X-ray diagnostic apparatus 1 accordingto the first embodiment makes it possible to instantly check eachobject.

Furthermore, according to the first embodiment, a three-dimensionalimage is a volume rendering image or an MPR image. Therefore, the X-raydiagnostic apparatus 1 according to the first embodiment can display theobject that is taken during a rotational acquisition as variousthree-dimensional images.

Second Embodiment

Although the first embodiment is explained above, various differentembodiments other than the above-described first embodiment may beimplemented.

In the above-described first embodiment, an explanation is given of acase where rotational acquisitions are performed twice after a contrastagent is injected. However, there is no limitation on the embodimentand, for example, there may be a case where rotational acquisitions areperformed three times or more. FIG. 8 is a diagram that illustrates anexample of a rotational acquisition of the X-ray diagnostic apparatusaccording to a second embodiment. FIG. 8 illustrates a case where arotational acquisition is performed once more after the rotationalacquisitions illustrated in FIG. 3. Specifically, FIG. 8 illustrates,for example, a case where the mask image and the first contrast imageare acquired under the same X-ray generation condition, the pulse widthof X-rays that are generated by the X-ray generator 11 is changed forthe second contrast image, and the pulse width is further changed forthe third contrast image.

For example, in the X-ray diagnostic apparatus 1, as illustrated in FIG.8, after the acquisition illustrated in FIG. 3, the second contrastimage is acquired and then, after a specific time (the time that isdifferent from the first and the second times) further elapses from thestart of imaging, the C-shaped arm 13 is rotated (forward) 60 degreesper second (arm rotation: 60°/sec), the projection angle is changed at afixed frame rate (frame rate: 60 fps), and the third contrast image of200 frames is acquired at an interval of 1 degree. Here, the conditionsetting unit 331 changes the X-ray generation condition to acquire thethird contrast image. For example, the condition setting unit 331changes “the pulse width” from “6 msec” to “4 msec” to capture the thirdcontrast image. Specifically, the acquisition control unit 27 causes thethird contrast image of 200 frames to be acquired with “the tubevoltage: 100 kV”, “the tube current: 250 mA”, “the pulse width: 4 msec”,“the tube focus size: Focus Middle (0.6 mm)”, and “the beam filter: Al1.8 mm”. The acquired third contrast image of 200 frames is convertedinto digital signals by the A/D conversion unit 21 and is stored in theimage memory 22.

For example, if “the pulse width” is changed like the third contrastimage of FIG. 8, the correction control unit 332 causes a subtractionoperation to be performed on the mask image and the third contrast imageby using the following Equation (7). Here, DSA_(θ)(x, y), MASK_(θ)(x,y), and CONT3_(θ)(x, y) in Equation (7) represent subtraction data, themask image, and the third contrast image. Furthermore, “θ” in Equation(7) represents the rotation angle. Moreover, a subtraction operation isperformed on the first contrast image and the second contrast image byusing the same equation as that in the first embodiment.

$\begin{matrix}{{{DSA}_{\theta}\left( {x,y} \right)} = {\log_{e}\left( {- \frac{3 \times {CONT}\; 3_{\theta}\left( {x,y} \right)}{{MASK}_{\theta}\left( {x,y} \right)}} \right)}} & (7)\end{matrix}$

For example, as illustrated in FIG. 8, if a subtraction is performed onthe mask image acquired with “the pulse width: 12 msec” and the thirdcontrast image acquired with “the pulse width: 4 msec”, the subtractionunit 23 generates subtraction data on the third contrast image by usingthe equation in which the third contrast image is multiplied by thecorrection factor “3” as represented by Equation (7). Specifically, thesubtraction unit 23 reads, from the image memory 22, 200 frames of themask image and 200 frames of the third contrast image and performs asubtraction on the sets of projection data of a corresponding rotationangle by using Equation (7), thereby generating subtraction data on thethird contrast image.

As described above, after sets of subtraction data on the first contrastimage, the second contrast image, and the third contrast image aregenerated, the three-dimensional reconstruction unit 31 reconstructsvolume data from each set of subtraction data, and the three-dimensionalimage processing unit 32 generates a three-dimensional image from eachset of reconstructed volume data. Then, the display control unit 333causes the display unit 40 to display the generated three-dimensionalimage. Furthermore, if rotational acquisitions are performed three timesor more as described above, each of the operations according to themodified examples 1 to 5 of the above-described first embodiment can beperformed.

An explanation is given above of an example of the operation of theX-ray diagnostic apparatus 1 according to the second embodiment. In theabove-described example, an explanation is given of a case where thepulse width for acquiring the third contrast image is narrower than thepulse width for acquiring the second contrast image and the pulse widthfor acquiring the second contrast image is narrower than the pulse widthfor acquiring the first contrast image. This embodiment is applied toacquiring of, for example, hepatic arteries or arteries of the brain.For example, proper hepatic arteries, internal carotid arteries,vertebral arteries, or the like, are acquired with the first contrastimage, hepatic veins, capillary blood vessels, or the like, are acquiredwith the second contrast image, and corona enhancement or veins of thebrain are acquired with the third contrast image.

In the above-described embodiment, an explanation is given of a casewhere the amount of X-rays is changed by changing the pulse width;however, there is no limitation on the embodiment, and there may be acase where the amount of X-rays is changed by changing the tube current.Furthermore, there may be a case where each of the tube current and thepulse width is changed.

In the above-described embodiment, an explanation is given of a casewhere one or two of the tube voltage, the tube current, the pulse width,the X-ray tube focus size, and the beam filter is changed. However,there is no limitation on the embodiment, and there may be a case wherea change is made to any combination of them. In such a case, acombination of the above-described corrections is performed.

In the above-described embodiment, an explanation is given of a casewhere the X-ray generation condition is set as an imaging condition foreach rotational acquisition; however, there is no limitation on theembodiment. For example, the required image quality level is related tothe function for a reconstruction. Therefore, an image reconstructioncondition may be set as an imaging condition for a case of areconstruction of subtraction data on the first contrast image and for acase of a reconstruction of subtraction data on the second contrastimage. Specifically, during rotational acquisitions that are performedmultiple times, the condition setting unit 331 further changes areconstruction condition in accordance with the purpose of therotational acquisition. Then, the three-dimensional reconstruction unit31 reconstructs an image under the reconstruction condition thatcorresponds to the required image quality level.

For example, an image quality level of veins of a cephalic region islow; therefore, if they are processed by using a high-pass filter as isthe case with arteries, noise is increased. Therefore, during rotationalacquisitions that are performed multiple times, when the rotationalacquisition is performed for an image from which a venous phase isextracted and an image from which an arterial phase is extracted, thecondition setting unit 331 sets a reconstruction condition toreconstruct the image from which a venous phase is extracted by using aweakened high-pass filter compared to the case of a reconstruction ofthe image from which an arterial phase is extracted. Then, when veins ofa cephalic region are reconstructed, the three-dimensionalreconstruction unit 31 performs an operation by using a weakenedhigh-pass filter compared to the case of a reconstruction of arteries,whereby noise is reduced. Furthermore, as contrast-agent densityinformation with regard to a capillary blood vessel image is generallyextremely little, if a reconstruction is performed in the same manner asarteries, noise is increased. Therefore, during rotational acquisitionsthat are performed multiple times, if the rotational acquisition isperformed for an image from which a capillary blood vessel phase isextracted and an image from which a venous phase is extracted, thecondition setting unit 331 sets a reconstruction condition toreconstruct the image from which a capillary blood vessel phase isextracted by using a weakened high-pass filter compared to the case of areconstruction of the image from which a venous phase is extracted.Then, in the case of a reconstruction of capillary blood vessels, thethree-dimensional reconstruction unit 31 performs an operation by usinga weakened high-pass filter compared to the case of a reconstruction ofveins, whereby noise is reduced.

Furthermore, for example, in the case of an identification of ahepatocellular tumor in an early stage, the condition setting unit 331sets a reconstruction condition that is different from that in the caseof an identification of a hepatocellular tumor in a middle stage or ahepatocellular tumor in a late stage. Here, a hepatocellular tumor hasstages, and the contrast during the contrast enhancement is changed froma hepatocellular tumor in an early stage to a hepatocellular tumor in amiddle stage and then a hepatocellular tumor in a late stage. Forexample, in the case of a hepatocellular tumor in an early stage, thecontrast enhancement is not different from that of normal hepatic cells,and the contrast is low. Specifically, with regard to a hepatocellulartumor in an early stage, low-contrast information is dominant. For thisreason, during rotational acquisitions that are performed multipletimes, when the rotational acquisition is performed for an image fromwhich a hepatocellular tumor in an early stage is extracted and an imagefrom which a hepatocellular tumor in a middle stage or a hepatocellulartumor in a late stage is extracted, the condition setting unit 331 setsa reconstruction condition to reconstruct the image from which ahepatocellular tumor in an early stage is extracted by using a weakenedhigh-pass filter compared to the case of a reconstruction of the imagefrom which a hepatocellular tumor in a middle stage or a hepatocellulartumor in a late stage is extracted. Then, the three-dimensionalreconstruction unit 31 performs an operation by using a weakenedhigh-pass filter compared to the case of a reconstruction of ahepatocellular tumor in a middle stage or a hepatocellular tumor in alate stage, whereby noise is reduced. Furthermore, the X-ray generationcondition for acquiring a hepatocellular tumor in an early stage is setsuch that the amount of X-rays is increased as is the case with theX-ray generation condition for acquiring a hepatocellular tumor in amiddle stage or a hepatocellular tumor in a late stage. Specifically, toidentify a hepatocellular tumor in an early stage or a hepatocellulartumor in a middle and subsequent stage, the reconstruction conditionsare different although the X-ray generation conditions are the same.

Furthermore, in the above-described embodiment, an explanation is givenof a case where, after a mask image is acquired, the C-shaped arm 13 isrotated in reverse and is returned to a rotation start position;however, there is no limitation on the embodiment. For example, after amask image is acquired, the C-shaped arm 13 may be rotated in reverse sothat the first contrast image is acquired.

Another Embodiment

The X-ray diagnostic apparatus illustrated in the description of thefirst embodiment and the second embodiment may be configured asillustrated in FIG. 9, for example. FIG. 9 is a diagram that illustratesan example of the configuration of an X-ray diagnostic apparatus 400according to another embodiment.

As illustrated in FIG. 9, the X-ray diagnostic apparatus 400 accordingto the other embodiment includes an X-ray acquisition mechanism 410 andan image processing device 420. The X-ray acquisition mechanism 410 andthe image processing device 420 correspond to the X-ray acquisitionmechanism 10 and the image processing device 100 illustrated in FIG. 1,respectively.

As illustrated in FIG. 9, the X-ray acquisition mechanism 410 includesan X-ray generator 411, an X-ray detector 412, a C-shaped arm 413, and abed 414, and the X-ray acquisition mechanism 410 is connected to aninjector 50. The X-ray generator 411, the X-ray detector 412, theC-shaped arm 413, and the bed 414 illustrated in FIG. 9 correspond tothe X-ray generator 11, the X-ray detector 12, the C-shaped arm 13, andthe bed 14 illustrated in FIG. 1, respectively.

As illustrated in FIG. 9, the image processing device 420 includes anA/D converter 421, storage circuitry 422, subtraction circuitry 423,filtering circuitry 424, affine transformation circuitry 425, LUTcircuitry 426, acquisition control circuitry 427, scattered-raycorrection circuitry 428, beam-hardening correction circuitry 429, ringcorrection circuitry 430, three-dimensional reconstruction circuitry431, three-dimensional image processing circuitry 432, processingcircuitry 433, and a display 40.

The A/D converter 421 corresponds to the A/D conversion unit 21illustrated in FIG. 1, and the storage circuitry 422 corresponds to theimage memory 22 illustrated in FIG. 1. The subtraction circuitry 423corresponds to the subtraction unit 23 illustrated in FIG. 1 andperforms the processing at Step S106 illustrated in FIG. 2. Thefiltering circuitry 424, the affine transformation circuitry 425, andthe LUT 426 correspond to the filtering unit 24, the affinetransformation unit 25, and the LUT 26 illustrated in FIG. 1,respectively. The acquisition control circuitry 427 corresponds to theacquisition control unit 27 illustrated in FIG. 1 and performs theprocessing at Step S101, Step S103, and Step S105 illustrated in FIG. 2.The scattered-ray correction circuitry 428, the beam-hardeningcorrection circuitry 429, and the ring correction circuitry 430correspond to the scattered-ray correction unit 28, the beam-hardeningcorrection unit 29, and the ring correction unit 30 illustrated in FIG.1, respectively. The three-dimensional reconstruction circuitry 431corresponds to the three-dimensional reconstruction unit 31 illustratedin FIG. 1 and performs the processing at Step S107 illustrated in FIG.2. The three-dimensional image processing circuitry 432 and the display40 correspond to the three-dimensional image processing unit 32 and thedisplay unit 40 illustrated in FIG. 1, respectively.

The processing circuitry 433 corresponds to the control unit 33illustrated in FIG. 1 and performs a condition setting function 434, acorrection control function 435, and a display control function 436. Theprocessing circuitry 433 is an example of processing circuitry describedin the Claims. The condition setting function 434 is a functionimplemented by the condition setting unit 331 illustrated in FIG. 1. Thecorrection control function 435 is a function implemented by thecorrection control unit 332 illustrated in FIG. 1. The display controlfunction 436 is a function implemented by the display control unit 333illustrated in FIG. 1.

For example, each of the respective processing functions performed bythe condition setting function 434, the correction control function 435,and the display control function 436, which are components of theprocessing circuitry 433 illustrated in FIG. 9, is stored in the storagecircuitry 422 in a form of a computer-executable program. The processingcircuitry 433 is a processor that loads programs from the storagecircuitry 422 and executes the programs so as to implement therespective functions corresponding to the programs. In other words, theprocessing circuitry 433 that has loaded the programs has the functionsillustrated in the processing circuitry 433 in FIG. 9. That is, theprocessing circuitry 433 loads a program corresponding to the conditionsetting function 434 from the storage circuitry 422 and executes theprogram so as to perform the same processing as that of the conditionstetting unit 331. The processing circuitry 433 loads a programcorresponding to the correction control function 435 from the storagecircuitry 422 and executes the program so as to perform the sameprocessing as that of the correction control unit 332. The processingcircuitry 433 loads a program corresponding to the display controlfunction 436 from the storage circuitry 422 and executes the program soas to perform the same processing as that of the display control unit333.

For example, Step S105 illustrated in FIG. 2 is a step that isimplemented by the processing circuitry 433 loading the programcorresponding to the condition setting function 434 from the storagecircuitry 422 and executing the program. Step S108 illustrated in FIG. 2is a step that is implemented by the processing circuitry 433 loadingthe program corresponding to the display control function 436 from thestorage circuitry 422 and executing the program.

In FIG. 9, the processing functions performed by the condition settingfunction 434, the correction control function 435, and the displaycontrol function 436 are described as being implemented in the singleprocessing circuitry 433. The functions, however, may be implemented byconfiguring processing circuitry by combining a plurality of separateprocessors and causing each of the processors to execute a program.

The term “processor” used in the above description means, for example, acentral preprocess unit (CPU) and a graphics processing unit (GPU), orcircuitry such as an application specific integrated circuit (ASIC), aprogrammable logic device (for example, a simple programmable logicdevice (SPLD)), a complex programmable logic device (CPLD), and a fieldprogrammable gate array (FPGA). The processor implements a function byloading and executing a program stored in storage circuitry. Instead ofbeing stored in storage circuitry, the program may be built directly incircuitry of the processor. In this case, the processor implements afunction by loading and executing the program built in the circuitry.The processors in the present embodiment are not limited to a case inwhich each of the processors is configured as a single circuit. Aplurality of separate circuits may be combined as one processor thatimplements the respective functions. Furthermore, the componentsillustrated in FIG. 9 may be integrated into one processor thatimplements the respective functions.

As described above, according to the first embodiment and the secondembodiment, the X-ray diagnostic apparatus of the embodiment can acquirethe optimum image data for each rotational acquisition.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An X-ray diagnostic apparatus comprising: asupport frame that supports an X-ray generator and an X-ray detector;and processing circuitry configured to, when rotational acquisitions areperformed multiple times after a contrast agent is injected one time,previously set a generation condition of an X-ray that is generated bythe X-ray generator for each of the rotational acquisitions, therotational acquisition being performed while the support frame isrotated around a subject.
 2. The X-ray diagnostic apparatus according toclaim 1, wherein the rotational acquisitions are automatically performedmultiple times after the contrast agent is injected once.
 3. The X-raydiagnostic apparatus according to claim 1, wherein the processingcircuitry sets the generation condition of the X-ray such that, out ofthe rotational acquisitions that are performed multiple times, a totalamount of X-ray radiation during a second rotational acquisition that isperformed after a first rotational acquisition is nearly equal to ormore than twice or nearly equal to or less than ½ of a total amount ofX-ray radiation during the first rotational acquisition.
 4. The X-raydiagnostic apparatus according to claim 1, wherein, when a rotationalacquisition is performed on a capillary blood vessel phase or a venousphase of the subject, the processing circuitry sets the generationcondition of the X-ray such that an amount of X-rays is decreasedcompared to other phases.
 5. The X-ray diagnostic apparatus according toclaim 1, wherein, when a rotational acquisition is performed on anarterial phase of the subject, the processing circuitry sets thegeneration condition of the X-ray such that an amount of X-rays isincreased compared to other phases.
 6. The X-ray diagnostic apparatusaccording to claim 1, wherein the processing circuitry sets at least oneof a tube voltage, a tube current, a pulse width, an X-ray tube focussize, and a beam filter as the generation condition of the X-ray foreach of the rotational acquisitions.
 7. The X-ray diagnostic apparatusaccording to claim 1, wherein the processing circuitry is furtherconfigured to correct data that is acquired by the X-ray detector inaccordance with the generation condition of the X-ray that is set by theprocessing circuitry.
 8. The X-ray diagnostic apparatus according toclaim 7, wherein, when a subtraction operation is performed by usingprojection data of a mask image and projection data of a contrast imagethat are acquired under different generation conditions, the processingcircuitry corrects at least one of the projection data of the mask imageand the projection data of the contrast image such that the subtractionoperation is performed by using sets of projection data for which thegeneration conditions are matched.
 9. The X-ray diagnostic apparatusaccording to claim 7, wherein, when a subtraction operation is performedby using reconstruction data that is reconstructed from projection dataof a mask image and reconstruction data that is reconstructed fromprojection data of a contrast image that are acquired under differentgeneration conditions, the processing circuitry corrects at least one ofthe reconstruction data that is reconstructed from the projection dataof the mask image and the reconstruction data that is reconstructed fromthe projection data of the contrast image such that the subtractionoperation is performed by using sets of reconstruction data for whichthe generation conditions are matched.
 10. The X-ray diagnosticapparatus according to claim 7, wherein, when at least one of the tubevoltage and the beam filter is different during multiple rotationalacquisitions, the processing circuitry corrects difference between setsof data due to beam quality.
 11. The X-ray diagnostic apparatusaccording to claim 10, wherein the processing circuitry correctsdifference between sets of data due to the beam quality on a pixel bypixel basis.
 12. The X-ray diagnostic apparatus according to claim 1,wherein the processing circuitry is further configured to cause adisplay to display multiple three-dimensional images that are takenduring rotational acquisitions under X-ray generation conditions thatare set by the processing circuitry.
 13. The X-ray diagnostic apparatusaccording to claim 12, wherein the processing circuitry displays themultiple three-dimensional images in fusion.
 14. The X-ray diagnosticapparatus according to claim 13, wherein the processing circuitrydisplays the three-dimensional images in different colors.
 15. The X-raydiagnostic apparatus according to claim 13, wherein thethree-dimensional images are volume rendering images or MPR images. 16.The X-ray diagnostic apparatus according to claim 1, wherein, during therotational acquisitions that are performed multiple times, theprocessing circuitry changes a reconstruction condition in accordancewith a purpose of the rotational acquisitions.
 17. The X-ray diagnosticapparatus according to claim 16, wherein, during the rotationalacquisitions that are performed multiple times, when a rotationalacquisition is performed for an image from which a venous phase isextracted and an image from which an arterial phase is extracted, theprocessing circuitry sets a reconstruction condition to reconstruct theimage from which a venous phase is extracted by using a weakenedhigh-pass filter compared to a case of a reconstruction of the imagefrom which an arterial phase is extracted.
 18. The X-ray diagnosticapparatus according to claim 16, wherein, during the rotationalacquisitions that are performed multiple times, when a rotationalacquisition is performed for an image from which a hepatocellular tumorin an early stage is extracted and an image from which a hepatocellulartumor in a middle stage or a hepatocellular tumor in a late stage isextracted, the processing circuitry sets a reconstruction condition toreconstruct the image from which a hepatocellular tumor in an earlystage is extracted by using a weakened high-pass filter compared to acase of a reconstruction of the image from which a hepatocellular tumorin a middle stage or a hepatocellular tumor in a late stage isextracted.